Winfield Peak-Antero

Region West, Rocky Mountains
Mineral systems
Deposit types
Critical minerals
Other minerals

Information leading to the delineation of this focus area

Basis for focus area The focus area encompasses of the Winfield Peak Mo porphyry deposit and the Mt. Antero beryllium pegmatites (latitude 38.6739, longitude -106.2469). These deposits occur in neighboring Climax-type porphyry systems that have been eroded to different levels. Since Climax-type porphyry systems commonly occur in clusters, a 15 km buffer was applied to Winfield Peak and Mt. Antero to encompass undiscovered occurrences in adjacent areas. The focus area boundary at Mt. Antero includes the edge of the Tomichi Copper Molybdenum Project (far southwest edge, west side of the continental divide near Vulcan Mountain). An additional focus area may need to be added for this deposit (current exploration and NI 43-101; Gray and Sim, 2017).
Identified resources Identified molybdenum resource; historical production of beryllium (beryl) and fluorite.
Production Unknown.
Status Past mining.
Estimated resources 1,800 million tons at 0.024% Mo at Winfield Peak/Middle Mountain (Ranta, 1974).
Geologic maps Brock and Barker (1972), scale 1:62.500: Shroba and others (2014), scale 1:24,000; Tweto and Reed (1973), scale 1:62.500; Tweto, Steven and others (1976), scale 1:250,000; Ranta (1974), scale unknown; Scott and others (1975), scale 1:62.500; Shannon and McCalpin (2006), scale 1:24,000; McCalpin and Shannon (2005), scale 1:24,000; Tweto, Moench and Reed (1976), scale 1:250,000; Van Alstine and Cox (1969), scale 1:24,000; Fridrich and others (1998), scale 1:50,000; Kellogg and others (2017), scale 1:50,000.
Geophysical data Inadequate aeromagnetic coverage, partly (<50%) adequate aeroradiometric coverage.
Favorable rocks and structures Rhyolite porphyry, quartz monzonite, granitic plutons.
Deposits Beryllium: California mine (MRDS dep_id: 10108192), Parakeet mine (MRDS dep_id: 10017015). Fluorite: numerous, including Browns Canyon district (MRDS dep_id: 10013778), Mt. Antero pegmatites, Winfield mining district (La Plata mining district-not to be confused with the other La Plata district in southwest Colorado), Tomichi deposit (USMIN Site_ID: CO00050), Tomichii district (USMIN Site_ID: CO00051).
Evidence from mineral occurrences MRDS; USMIN.
Geochemical evidence Winfield Peak porphyry Mo prospect contains sphalerite, wolframite, beryl, bismuthinite, and aikinite (Pb, Bi-sulfide).
Geophysical evidence Porphyry Mo deposits are believed to emanate from larger silicic plutons that can create gravity lows. However, the Middle Mountain/Winfield porphyries intrude the Eocene-Paleocene Twin Lakes pluton, and it is unclear how of the silicic material actually pre-dates mineralization.
Evidence from other sources State-wide trend of similar occurrences (Climax-type).
Comments Several exploration studies associated with Middle Mountain and Winfield Peak. Molybdenum mineralization is associated with rhyolite porphyry and granite stocks intruded into Twin Lakes quartz monzonite. Early rhyolite porphyry stock and radial dike system occur near the center of concentric zones of hydrothermal alteration and mineralization that includes a Climax-type Mo shell at Middle Mountain. Early stage alteration and mineralization zones at Winfield Peak are roughly centered on a body of granite porphyry which may be the source of Mo. Mineralization is mainly confined to the phyllic and argillic zones which broadly overlap near a shear zone. Late base-meal veins and a breccia pipe are associated with rhyolites. These later stage altered rhyolites and breccias are interpreted as the surface expression of a Mo-bearing granitic pluton at depth (Ranta, 1974). Rhenium, Sc, N, and W are inferred from the mineral system/deposit type table (Hofstra and Kreiner, 2020).
Cover thickness and description Exposed to shallow cover.
Authors Ryan D. Taylor, Albert H. Hofstra, Joshua M. Rosera, V.J.S. (Tien) Grauch.
New data needs 1:24,000 scale geologic mapping and geophysics.
Geologic mapping and modeling needs 1:24,000 scale geologic mapping needed in the following quadrangles: Saint Elmo, Garfield, Cumberland Pass, Mount Yale, Mount Elbert, Independence Pass, Pieplant, Winfeld, and Tincup.
Geophysical survey and modeling needs Most of the northern part of this focus area is covered by Wilderness Areas, which is off limits to new airborne geophysics, and it would be difficult to fly around. New aeromagnetic and radiometric surveys for the southern area would help delineate bedrock units and alteration as well as rift-related faults.
Digital elevation data needs Lidar in progress.